First of all a g-23 on this plane is not safe at all> this plane flies great on a 61 2-stroke. That kind of torque on that airframe will cause the fuselage to rip apart. Look at the plans........I would only go with a 90 at tops, and I overpower everything I have. I have a Telemaster Sr. with a K and B 65 sportster. It will almost take off strait up with a 13 inch prop.
Remember safety first............................................. ...................Now for the wing; Why do you want a 2 piece wing? for transporting it?
Hobby Lobby made a arf telemaster Sr. a few years back which incorporated a 2 piece wing with a joiner similar to the one in your kit. You just slip the wing together till the roots butt together, start putting bands on and fly. Your friend that told you to build a box was correct if this is what you really want to do.
Problem> what to do about front and rear joiner
My best suggestion would be to enjoy the plane as it was intended to be constructed. It has stood the test of time. The wing will stand up nicely in any room that is 8 ft. or higher.